From Wikipedia: According to the 2000 censuses, the number of ‘Miao’ in China was estimated to be about 9.6 million. The Miao nationality includes Hmong people as well as other culturally and linguistically related ethnic groups who do not call themselves Hmong. These include the Hmu, Kho (Qho) Xiong, and A-Hmao. The White Miao (Bai Miao) and Green Miao (Qing Miao) are Hmong groups.
Here is something I found about the silver hats on display: Silver Ornaments of the Miao Ethnic Group
And an exhibition by the Bowers Museum, on Miao silver: https://www.bowers.
A short video:
Miao Textiles at the Minneapolis Institute of Arts